Ultra high frequency radio receiver



July 2, 1940.

W. L. CARLSON ULTRA HIGH FREQUENCY RADIO RECEIVER Filed March 51, 1938. 2 sheets-sheet 1 July 2, 1940.

W. L. CARLSON ULTRA HIGH FREQENCY RADIO RECEIVER Filed March 31, 1938 2 Sheets-Sheet 2 /a/za 1 3 rwentor dttorneg Patented July 2, 1940 ,PATENT oEFIcE 2,200,390 q ULTRA HIGH FREQUENOY mimo- RECEIVER Wendeu L. Carlson, Hadaoneld, N. J., assignor to Radio Corporation of America, a corporation of Delawarew v Application March 31,

9 Claims.

The present invention relates to ultra high frequency radio receivers, and has for its Object to provide an improved tuning system for ultra high frequency receivers which includes an intermediate frequency amplifier tunable to a plurality of differing frequencies within a predetermined wave band, having a predetermined relation'to the wave band response within which the receiver is operable.

It is also an object of the present invention to provide an intermediate frequency amplifier for an ultra high frequency receiver, which is tunable to a plurality of differing intermediate frequencies within a predetermined wave band and to provide the sole selective variable tuning means for the receiving system.

It is a still further object of the present invention to provide an intermediate frequency ampliiier for ultra high frequency radio receiving systems which is responsive to a plurality of intermediate frequencies, and an improved interstage coupling and tuning means therefor.

The invention will, however, be better understood from the following description, when considered in connectionv with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings,

Figure 1 is a schematic circuit diagram of an intermediate frequency amplifier for an ultra high frequency superheterodyne receiver, embodying the invention, and

Figure 2 is a series of curves illustrating certain of the frequency response characteristics of the amplifier shown in Fig. 1.

Referring to Fig. 1, the intermediate frequency amplifier comprises a series of cascade connected intermediate frequency amplier electric discharge devices or tubes 5, 6, 'I and 8 and tuned coupling transformers. 9, I0, II and I2, the last being coupled to the second detector I3.

The primaries I4 and the secondaries I5 of the successive coupling transformers are tunable by meansI of shunt capacitors I6 to a predetermined intermediate frequency which is a low` percentage or a sub-multiple of the highest signal frequency to be received, such as 10.5'megacycles, for example, which is preferably substantially ten percent of the highest frequency Within which the receiving system is responsive. In the present example, the receiving system-may be considered to have a response range of `from 105 down to 100 megacycles.

The signal receiving means or input tuning system and oscillator 'for the superheterodynel re- 1938, Serial No. 199,199

(Cl. Z50-20) ceiver are indicated at I1 and the tube 5 may be considered as the first detector or mixed tube which receives signals on a grid I8 and oscillations from local generator on the lgrid I9. The r-f tuning system is broadly tuned for response within the range of from 100 to 105 megacycles without manual tuning and any signals within that range are applied to the second detector to combine with the locally generated oscillations to produce an intermediate frequency within the range of from 10 to 10.5 megacycles.` The local generator or oscillator is ypreferably crystal controlled or otherwise arranged to give high stability, that is, Vthe same order of stability as present on the received signal carrier frequency.

` In order to select ultra high frequency signals, it has been found to be most dependable and accurate to provide adjustable' tuning at low frequencies, after heterodyne detection, with fixed tuned r-f and local oscillator circuits. lAccordingly, the intermediate frequency amplifier is caused lto be adjustably tunable within the lower frequency range in a series of steps, for example, vin live steps, as indicated in Fig. 2, for a relatively sharp response about mean frequencies at 10.0, 10.125, 10.25, 10.375 and 10.5 megacycles. A greater or lesser number of tuning adjustment points may be arranged in the amplifier to cover a greater or lesser number of receivable signal channels within the response range of thereceiving system as may be desirable. 'I'he live preselection points of tuning and the frequency range referred to are shown, only by way of example, as being one of several present preferred tuning points in a predetermined high frequency tuning range.

The primaries and secondaries I4 and I5 of the interstage coupling transformers are further tunable to an initial adjustment by movable magnetite cores indicated at and 2I, each associated with one of the windings for varying the inductance thereof. The interstage coupling means are further tunable to the successive lower frequency response bands about the selected mean frequencies by adding xed inductances 23 to 26, inclusive, in pairs to the primary and secondary circuits in connection with the 10W side of the primary and secondary windings I4 and I5.

This is accomplished by movable tapswitch connections 2'I in the secondary circuit and 28 in the primary circuit, in connection with taps 29 to 33, inclusive, along the s'eries'connected coils` 23 to 26, inclusive, to progressively include an additional coil in the primary and in the sec- Iii) vio

ondary circuit with each succeeding adjustment from the taps 29 toward the taps 33.

The mutual coupling between the primary and secondary isI increased as additional inductance is included in the two circuits, by the presence of coupling capacitors 34 connecting the low sides of the main primary and secondary windings E4 and I5.

The coupling capacitors 34 are permanently connected-betweenthelow potential sides of the main primary and secondary windings or between the initial primary and secondary switching taps, as shown, and Aserve-to. increase the *i coupling between the primary and secondary cir-y cuits foi each interstage coupling transformer asV the taps 21 and 28 are moved progressively to include additional inductance in each circuit.

This circuit arrangement provides a primary circuit and a secondary circuit, in this case an output anode circuit and an input grid circuit,

for each intermediate frequency amplifier stage, comprising the primary and secondary of a coupling transformer, the windings of which are tunable by means of movable magnetite or ferromagnetic cores and by shunt capacitors. l

` In addition, the low potential ends of each primary and secondary are connected with additional coupling windings in pairs, the windings for the primary and secondary being in series and having a switch connection for including Ithe shunt tuning capacitor in parallel with additional coupling windings in` each circuit.

A coupling capacitor connected with the low `potential ends of the primary and secondary provides increasing coupling as the inductance in each circuit is increased, maintaining a relatively high gain throughout the tuning range and holding up the gain at the low frequency end of the range appreciably. 'I'his is shown in Fig. 2 in the curves 35-30, inclusive, which represent the response characteristic of each stage coupling u preferably supplied through connection leads indicated at 4i and 42 to the tap switches 21 and y28, suitable filter means being provided as indicated bythe series resistors 43 and the filter capacitors 44for each circuit.

In an amplifier of this type it has been found preferable to provide a separate channel ampli-l fier and rectifier for the supply of automatic volume controlpotentials. This amplifier channel is tunable for broad response throughout the tuning range of the main amplifier channelwhich, in this case, is from 10 to 10.5 megacycles.

. Such a separate channel amplifier is indicated by the amplifier tube 45 in which is combined a diode rectifier 46 providing the a. v. c. potentials. In ,the present arrangement, the secondary for the third i-f amplifier tube 8 is tapped,.as indicated at 41, for supplying signals to the ampliiier tube 8, while the entire secondary voltage is taken throughv the connection lead 49 and ap- `plied to the control-.grid of the a. v. c. am-

plier 45. The output of the amplifier is coupled through a broadly tuned coupling transformer 5i with the a. V. c. diode rectifier anode 56 which has a cathode 52 in common with the amplifier in the same envelope. The cathode circuit is completed through ground and a diode output resistor 53 in series with the secondary 54 of the transformer 5i. An intermediate frequency by-pass capacitor 55 is provided for the resistor 53 and a. v. c. potentials are derived from the resistor through output leads 55.

- vIt will be noted that the primary and secondary `of the transformer 5l in the a. v. c. amplifier channel are tuned broadly without shunt capacitors, and the tuning response is further broadened by the use of a shunt resistor indicated at 51.

The main signal amplifying channel of the intermediate frequency amplifier is made substantially sharply responsive to a plurality of signal bands of relatively narrow range about mean intermediate frequencies corresponding to desired signal channels or broadcasting stations, while the separate channel a. v. c. amplifier is coupled into the amplier at a suitable point following the initial amplier stages, to respond broadly to signals in any of the selected bands, whereby a. v. c. ,potentials may be applied to the receiving system effectively for each of the signal receiving tuning adjustments.

Furthermore, by connecting the a. v. c. channel, as shown, amplification of the received signals for automatic volume control purposes is obtained while at the same time the selective tuning of the a. v. c. supply circuit and the additional means which would be required for that purpose is eliminated. u

'I'he second detector i3 is likewise a diode rectifier as indicated at 58, having an output resistor 59 to which is connected the control grid 60 of an amplifier included in the same envelope with the diode and having a common cathode 6I therewith. Rectied signals derived from the diode output resistor 59 are amplified by the amplifier 60 and derived therefrom from an output anode indicatedat 62 and an audio frequency output circuit 63. The receiving system may include further audio frequency amplifying apparatus, not shown.

In a practical embodiment of the tuning system, the switches 21 and 28 and the associated contacts 29 to 33 inclusive are provided by rotary tap switches preferably of the well-known ganged multiple section type at present used for wave band change control in receiving systems,

and the coupling windings 23 to 2S, inclusive, are mounted directly between the switch contacts substantially as indicated in kthe drawings, Fig. 1. This simplifies thev circuit connections for the windings and reduces the length of connection leads required for the series-connected coil system, since the switch contacts become, in effect, the coil terminals.

The intermediate frequency amplier is tunable at a lower frequency than the frequency of the signals to be received and each of the tuning steps is arranged to be a small percentage of thefrequency ofthe signal frequency lbeing received. With .this arrangement, the tuning system for the receiver and the oscillator may be fixed tuned for broad response in an ultra-high frequency band, such that the receiver may be tuned within that band at the relatively low intermediate frequencywith a high degree of stability of operation, since none of the ultra-high frequency. tuning circuits are disturbed or changed by the tuning operation.

In the present example, a tuning range of from 100 to 105 megacycles is obtainable with stable operation, and the tuning range of the intermediate frequency amplifier may be a relatively narlrow range of from 10 to 10.5 megacycles. While five tuning points have been shown in the present system, it should be appreciated that more or less may be provided for the same or wider over-all tuning range, as may be desired. The intermediate frequency amplifier is operable at a relatively low percentage of the freqtuency range within which signals are to be received and the system is particularly adapted for tuning in signal receiving ranges above 100 megacycles.

I claim as my invention:

1. The combination with a signal receiving system of an intermediate frequency amplifier comprising a plurality .of amplifier stages, an amplier tube and interstage coupling means therefor in each stage, said coupling means comprising a coupling transformer having a primary winding, a secondary winding, a coupling capacitor connected between the low potential ends of said windings. a, shunt tuning capacitor for each of said windings, additional coupling windings for said primary and secondary connected in series therewith at the low potential ends thereof, and selective switching means for progressively including said additional coupling windings in circuit with said primary and secondary and said shunt tuning capacitors to tune said amplifier progressively in a series of steps within a predetermined frequency range.

2. In an ultra high frequency superheterodyne receiver, an intermediate frequency amplifier comprising a plurality of amplifier stages, an amplifier tube and interstage coupling means there for in each stage, said coupling means comprising a coupling transformer having a primary winding, a secondary winding, a coupling capacitor connected between the low potential ends of said windings, a shunt tuning capacitor for each of said windings, additional coupling windings for said primary and secondary connected in series therewith at the low potential ends thereof, and selective switching means for progressively including said additional coupling windings in cir cuit with said primary and secondary and said shunt tuning capacitors to tune said amplifier progressively in a series of steps within a predetermined low frequency range, and means providing broad fixed tuning response for said receiver preceding said intermediate frequency amplifier, in an ultra high frequency range having a predetermined relation to said low frequency range whereby said intermediate frequency amplifier provides a signal selecting means for said receiver at mean frequencies corresponding to desired signal frequencies and at a fixed relatively low percentage of said signal frequencies.

3. The combination with a tuning system for an ultra high frequency radio signal receiver, of an intermediate frequency amplifier comprising a plurality of cascade connected amplifier tubes, means for tuning said amplifier in a plurality of spaced relatively narrow pass bands, comprising an interstage coupling transformer having a primary and a secondary, an anode circuit connected with the primary at the high potential side thereof, an input grid circuit connected with the high potential side of said secondary winding, a plurality of coupling windings connected in series with said primary and secondary and coupled in pairs, and means for progressively including said additional windings in circuit with said prin mary and secondary for tuning said amplifier to a plurality of differing submultiple frequencies of desired signal frequencies.

4. The combination with a tuning system for an ultra high frequency radio signal receiver, of an intermediate frequency amplifier comprising a -plurality of cascade connected amplifier tubes, means for tuning said amplifier in a plurality of spaced relatively narrow pass bands, comprising an interstage coupling transformer having a primary and a secondary, an anode circuit connected with the primary at the high potential side thereof, an input grid circuit connected with the high potential side .of said secondary winding, a plurality of coupling windings connected in series with said primary and secondary and coupled in pairs, and means for progressively including said additional windings in circuit with said primary and secondary for tuning said amplifier to a plurality of differing submulti-ple frequencies of desired signal frequencies, said primaries and secondaries being provided with movable tuning cores and said last named means including switch elements having contacts providing terminal connections for said additional windings.

5. In an ultra-high frequency radio signal receiving system, the combination of signal receiving means broadly responsive to a band of signal frequencies, an intermediate frequency amplifier including a plurality of amplifier tubes and interstage coupling means therefor, a first detector coupling said signal receiving means andl said intermediate frequency amplifier, said interstage coupling means providing the sole tuning means for said receiving system and being tunable conjointly to a plurality of differing intermediate frequencies, each of which is a low percentage of a selected frequency in the tuning range of said receiver, and said interstage coupling means each comprising a coupling transformer having a primary winding, a secondary winding, a coupling capacitor connected between the low potential ends of said windings, a shunt tuning capacitor for each of said windings, and additional coupling windings for said primaries and secondaries connected in series therewith at the low potential ends thereof, and selective switching means for progressively including said additional coupling windings in the circuit with said primary and secondary and said shunt tuning capacitors to tune said amplifier progressively in a series of steps Within a predetermined frequency range which is a small percentage of the frequency range to which said receiving system is responsive.

6. In an ultra-high frequency radio signal receiving system, the combination of signal receiving means broadly responsive to a band .of signal frequencies, an intermediate frequency amplifier including a plurality of amplifier tubes and interstage coupling means therefor, a first detector coupling said signal receiving means and said intermediate frequency amplifier, said interstage coupling means providing the sole tuning means for said receiving system and being tunable conjointly to a plurality of differing intermediate frequencies, each of which is a low percentage of a selected frequency in the tuning range of said receiver, means providing automatic volume control potentials for said receiving systern coupled to an intermediate interstage coupj..

ling means in said amplifier and comprising an Aamplifier tube, a rectifier, an-output circuit for said rectifier, and coupling means between said amplifier and rectier broadly responsive to signals within the tuning range of said intermediate frequency amplifier, whereby said automatic volume control means is effective for all tuning adjustments of said receiving system.

7. In a superheterodyne receiver for ultra-high frequency signals, the combination of a fixed.

tuned signal receiving system including an `oscillator and first detector broadly responsive to signals within a predetermined frequency range, an intermediate frequency amplifier coupled to said first detector, means for tuning said intermediate frequency amplifier through a low frequency range which is a small percentage of the tuning response range of said receiving system, said tuning means comprising interstage coupling transformers for said amplifier having primary and secondary windings tuned to a mean frequency response in a relatively narrow pass band which mean frequency is a small percentage of the highest frequency to be received in the tuning range .of the receiver, additional coupling windings for said primaries and secondaries in series therewith at the low potential ends thereof, and selective switching means for progressively including said additional coupling windings in circuit with said primaries and secondaries to tune said amplifier progressively in a series of steps at lower frequencies within the predetermined frequency range of the amplier.

8. In a superheterodyne receiver, a system for tuning said receiver in a relatively narrow frequency range above 100 megacycles, comprising tuning, oscillator and first detector means broadly responsive to signals in a frequency band of the order of 5 megacycles inwidth in said predetermined high frequency range to provide a predetermined intermediate frequency in a lower and narrower frequency range at frequencies substantially ten -per' cent of the frequencies in said signal receiving range, an intermediate frequency amplifier coupled to said first detector means, said amplierhaving interstage coupling means conjointly tunable in predeterminedl steps to a plurality of differing frequencies withinsaid low frequency range as the sole tuning control means for said receiver.-

9. In a superheterodyne receiver, a system for vtuning said receiverl in a relatively narrow frequency range above 100 megacycles,'comprising tuning, oscillator and first detector means broadly responsive to signals in said predetermined high frequency range to provide a predetermined intermediate frequency in a lower and narrower frequency range at frequencies substantially. ten per cent of the frequencies in said signal receiving range, yan intermediate frequency amplifier coupled to said first detector means, said amplifier having interstage coupling means conjointly tunable to a plurality of differing frequencies within said low frequency range as the sole tuning control means for said receiver, said intermediate frequency amplifier having interstage coupling transformers provided with movable magnetite cores and shunt tuning capacitors for tuning said transformers to the highest frequency in the low frequency tuning range, a capacitor providing coupling between the low potential ends of the primary and secondary windings of said transformers, additional coupling windings connected in circuit with said primary and secondary windings at the low potential ends thereof, and multiple Contact gang-controlled switch means for connecting said additional coupling windings progressively in circuit with said primary and secondary windings and said shunt tuning capac- .itors to tune said amplifier progressively to lower frequencies within said low frequency tuning range, said coupling windings being connected between the contacts of said switching means.

WENDELL L. CARLSON. 

